In a batch-type heat treating apparatus that performs a heat treatment, such as a film deposition process, an oxidation process or a diffusion process, to a number of semiconductor wafers collectively, process conditions, such as process temperature, process pressure and gas flow rate, are determined beforehand depending on the sort of a film to be formed and the film thickness, etc., and recipes describing the above process conditions are prepared. The operator selects a recipe corresponding to the sorts of a film and the film thickness, and the heat treatment apparatus operates under predetermined process conditions.
The heat treatment apparatus performs a treatment while controlling the process conditions, such as process temperature, process pressure, gas flow rate etc., so that they coincide with respective target values defined in the recipe. In order to perform the treatment, it is necessary to measure temperatures of the wafers, pressure in a heating furnace, gas flow rates and so on.
The pressure in the heating furnace can be measured relatively precisely by a pressure gauge. Similarly, the gas flow rate can be measured relatively precisely by a mass-flow controller having a flowmeter or the like disposed in a supply pipe. However, it is difficult to measure wafer temperatures. For example, a technique of accommodating a wafer holding a temperature sensor in the heating furnace is conceivable. In this case, however, it becomes impossible to build a semiconductor element on a wafer's portion equipped with the temperature sensor. Moreover, there is a possibility that impurities originated from the temperature sensor contaminate the whole interior of the heating furnace, reducing a yield ratio of semiconductor devices.
A technique for solving these problems is disclosed in Japanese Patent Publication JP2002-25997A and U.S. Pat. No. 5,517,594. With this technique, plural temperature sensors are arranged in a heating furnace. Based on the outputs of the temperature sensors and the electric power supplied to the heaters etc., temperatures of wafers are estimated momentarily by using a thermal model (mathematical model). The electric power supplied to the heaters is controlled by using the estimated values. According to this technique, it is possible to control a heat treatment apparatus while the temperatures of the wafers are estimated relatively precisely in non-contact manner.
The thermal model for the above apparatus is established as follows. First, a thermal model (standard model) is made for a standard apparatus. Then, the standard model is applied to apparatuses having the same structure. Next, setup work is performed to compensate for a slight equipment-difference (individual difference) between the standard apparatus and individual apparatuses. This work is carried out by performing a deposition process for setup by using each individual apparatuses, and by correcting the thermal model based on the difference between the deposited film thickness and the target film thickness so that the individual apparatuses can form films of the same thickness irrespective of the equipment-difference among the individual apparatuses.
The differences between the standard apparatus and the individual apparatuses include not only a difference relating to heat but also differences relating to gas flow rate and gas pressure. In other words, there are deviations in measurements of the pressure gauge and the gas flowmeter among the individual apparatuses.
Nevertheless, the conventional setup technique is constructed so that the thermal-model correction also absorbs equipment-differences derived from all the factors except heat, and eliminates the individual difference among the apparatuses in appearance, in order to form the identical films in all the apparatuses. Such a setup technique is very effective, because it is not necessary to perform in-depth analysis of the differences among the apparatuses in order to obtain apparatuses of substantially the same specification.
In the above conventional setup technique, however, the thermal situation of the apparatus is not clear in some cases. For instance, if the thermal model cannot absorb the equipment-differences, it is not clear which part of the apparatus causes a deviation in the processing result (e.g., deviation in film thickness in the deposition process). In other words, it is impossible to grasp the thermal characteristics of the individual apparatuses precisely.